Evening all, my 1.2HTP has just failed her MOT on "Exhaust carbon monoxide content after 2nd fast idle exceeds manufacturer's specified limits". A blast on the motorway didn't help, neither did some injector cleaner.

 

What do you reckon my options are 😞

Edited 16 December, 20196 yr by garibaldy

Any fault lights or codes?

Any loud farty noises consistent with upstream exhaust leaks?

Check the voltage on the lambda probe(s)?

My instinct would be to replace the pre cat lambda probe, it's probably drifted out of spec.

20 minutes ago, Wino said:

Any fault lights or codes?

Any loud farty noises consistent with upstream exhaust leaks?

 

Hi Wino - No farty noises, but every couple of months i have the following error which i reset with VCDS lite:

 

16804 -  Catalyst System; Bank 1: Efficiency Below Threshold
            P0420 - 006 -  Short to Plus - Intermittent

 

This has happened for almost 3 years.

Edited 16 December, 20196 yr by garibaldy

Possible Causes

• Leakage in Intake and/or Exhaust System
• Catalyst faulty
• Oxygen Sensor(s) faulty
• Oxygen Sensor(s) Control faulty

Possible Solutions

• Check Intake and Exhaust System for Leaks
• Check Catalyst
• Check Oxygen Sensor(s)
• Check Oxygen Sensor(s) Control
  • Perform Oxygen Sensor(s) Aging Check

9 minutes ago, garibaldy said:

 

Hi Wino - No farty noises, but every couple of months i have the following error which i reset with VCDS lite:

 

16804 -  Catalyst System; Bank 1: Efficiency Below Threshold
            P0420 - 006 -  Short to Plus - Intermittent

 

This has happened for almost 3 years.

 

Has the CO reading been getting steadily worse over those 3 years? Do you keep the printouts?

Been getting the same code occasionally on ours lately. I've got a 2nd hand much lower mileage genuine cat to fit prior to our next MOT, but haven't systematically ruled out other issues.

 

 

Air filter clean?

29 minutes ago, KenONeill said:

Check the voltage on the lambda probe(s)?

 

Cheers Ken, what is the tolerance on the sensor?

29 minutes ago, sepulchrave said:

My instinct would be to replace the pre cat lambda probe, it's probably drifted out of spec.

 

Nice one, thanks Sepulchrave is it a common fault?

16 minutes ago, RicardoM said:

Possible Causes

• Leakage in Intake and/or Exhaust System
• Catalyst faulty
• Oxygen Sensor(s) faulty
• Oxygen Sensor(s) Control faulty

Possible Solutions

• Check Intake and Exhaust System for Leaks
• Check Catalyst
• Check Oxygen Sensor(s)
• Check Oxygen Sensor(s) Control
  • Perform Oxygen Sensor(s) Aging Check

 

Thanks ricardoM - i had the front section of the exhaust/flexi replaced last year but it didn't stop the error code appearing.

@Wino i haven't kept the readouts 😞 , is a cat your gut feel? The mot test centre reckons on replacing the manifold.

9 minutes ago, TMB said:

Air filter clean?

 

@TMB i changed the air filter about 18 months ago. Although each time i remove the "engine cover/air filter" i'm always suspicious of the seal.

I suspect both pre and post oxygen/lambda sensors, one or both can fail which leads to over fueling, causing high co readings (engine ECU will revert back to very basic settings so the engine can keep running), also the error code your getting points to this fault, as the short to plus is symptomatic of a sensor not working correctly.

 

Best practice to change both, when one has failed the other won't be far behind.

17 minutes ago, garibaldy said:

@Wino i haven't kept the readouts 😞 , is a cat your gut feel? The mot test centre reckons on replacing the manifold.

 

It's my gut feel for ours, but not enough evidence about yours to say that. The precat (and postcat AFAIR) oxygen sensors on ours are reasonably recent and genuine, and I know there are no inlet manifold leaks (have you looked at your brake servo vac hose lately?). 

There have been minor leaks around the manicat connections both to head and downpipe at different times which I'm still struggling to completely overcome, so it could simply be related to those. But you don't seem to have those, it's easy to hear when you do.

 

How many miles on the odo?

 

 

Edited 16 December, 20196 yr by Wino

3 hours ago, garibaldy said:

 

Hi Wino - No farty noises, but every couple of months i have the following error which i reset with VCDS lite:

 

16804 -  Catalyst System; Bank 1: Efficiency Below Threshold
            P0420 - 006 -  Short to Plus - Intermittent

 

This has happened for almost 3 years.

 

Is the car mostly used for short trips, it could be that it needs a good cook up on a longer run, cheapest and quickest fix might be to just bung in a tankful of petrol and go for a long fast trip down the nearest motorway and back to get the whole system properly hot.

17 hours ago, sepulchrave said:

 

Is the car mostly used for short trips, it could be that it needs a good cook up on a longer run, cheapest and quickest fix might be to just bung in a tankful of petrol and go for a long fast trip down the nearest motorway and back to get the whole system properly hot.

Yes mostly short trips but I did take it for a drive up and down the M3 for about 40 miles before the MOT. 

21 hours ago, Wino said:

 

Has the CO reading been getting steadily worse over those 3 years? Do you keep the printouts?

Been getting the same code occasionally on ours lately. I've got a 2nd hand much lower mileage genuine cat to fit prior to our next MOT, but haven't systematically ruled out other issues.

 

 

 

I have found the printouts. 2 years ago there was an adivsory "Exhaust has a minor leak of exhaust gases front (flexy)". The first fast idle test failed with a reading of 0.393% and the second passed (just) at 0.292%. Last year it failed on emissions and she needed a new front exhaust section. Then passed and the CO reading was 0.04. This year it failed with a CO reading of  0.49%.

 

I thought that would be the end of the EML and error code but it wasn't. Car only covered 2,300 miles since the last MOT and mostly short journeys.

Got the car through the MOT using a bottle of this:

 

I'd go with the "Italian Tune up" as well  take it at 70mph for at least 60 miles in 4th and absolutely redden her ! A private road is very useful as well for up and down through the gears !

 

When you stop if she isn't making pinging noises as she cools then you haven't gave her enough wosskey!